You're heard of immigration? For the past 20 years, pret-near 100% of the increase in US population has been due to immigration and the first-generation children of immigrants. All USA-born demographic groups (white, black, Asian, USA-born Hispanic) have total fertility rates below replacement. The white American fertility rate has been below replacement for more than 30 years.

Nations that will not welcome babies are generally obliged to welcome immigrants. Whether you like it or not, a tide of mostly Western Hemisphere inflow (including illegal) has become out alternative to demographic implosion.

They aren't doing that in Western Europe, where in many countries the average couple has one child. They are close to stability in numbers due to islamic immigration and because the older generations, who still have siblings and cousins unlike the younger generation have not yet died.